The present invention provides a process for making 3-hydroxyalkanenitriles comprising the steps of reacting certain alkenylnitriles with benzyl alcohol in the presence of a base to form a 3-benzyloxyalkanenitrile adduct and then partially hydrogenating the adduct to form the 3-hydroxyalkanenitrile. The adduct may also be fully hydrogenated to form a 3-hydroxyaminoalkane.
The synthesis of hydroxyalkanenitriles from reactions of epoxides with HCN is known. For example in French patent 1446127 teaches the preparation of cyanohydrins by treating epoxides with HCN in the presence of an alkyl aluminum compound. 3-hydroxyalkanenitriles have also been prepared from 1,2-epoxides using halohydrin epoxidase of corynebacterium in JP-05317066.
Alkanolamines(which are also referred to herein as hydroxyaminoalkanes) have been prepared by reaction of alkylene oxides with ammonia in the presence of a variety of catalysts. For example, U.S. Pat. No. 5,633,408 teaches reacting the alkylene oxide with ammonia in the presence of ammonium carbonate; U.S. Pat. No. 5,599,999 teaches the reaction of alkylene oxide with ammonia in the liquid phase over a rare earth catalyst. Other methods for making alkanolamines starting from alkylene oxides include U.S. Pat. Nos. 4,567,303; 4,355,181; 4,605,769; 4,931,596, and JP-07033718A.
The present inventor wished to use a simple addition reaction using pentenenitriles as the starting material for the synthesis of the 3-hydroxyalkanenitriles. After much experimental work he found that routes used to add water to molecules such as acrolein and acrylonitrile did not provide a workable method for the synthesis of 3-hydroxyalkanenitriles starting from pentenenitriles. The object of the present invention is to provide routes to 3-hydroxyalkanenitriles and alkanolamines using a Michael-type addition reaction followed by hydrogenation.
The present invention provides a process for making 3-hydroxyalkanenitriles comprising the steps of reacting an alkenylnitrile, wherein the alkenylnitrile is an alkenyl-2-nitrile or an alkenylnitrile which under reaction conditions isomerizes to form an alkenyl-2-nitrile, in the presence of a base with benzyl alcohol to form a 3-benzyloxyalkanenitrile adduct and then partially hydrogenating the adduct in the presence of a trace amount of HCl to form 3-hydroxyalkanenitrile.
The present process may be run as a batch, semi-batch or a continuous process.
Acceptable bases for the present process include bases selected from the group consisting of alkali metal hydroxides, alkaline earth metal hydroxides, alkali metal carbonates, alkaline earth metal carbonates, tertiary amines, Lewis bases and strongly basic ion exchange resins.
The 3-hydroxyalkanenitrile product of the present invention may be converted into a hydroxyaminoalkane if, after the formation of the benzyloxyalkanenitrile adduct, the adduct is completely hydrogenated to form a 3-hydroxyaminoalkane.
The present invention provides a process for making 3-hydroxyalkanenitriles comprising the steps of reacting certain alkenylnitriles with benzyl alcohol in the presence of a base to form a 3-benzyloxyalkanenitrile adduct and then partially hydrogenating the adduct to form the 3-hydroxyalkanenitrile. The adduct may also be fully hydrogenated to form a 3-hydroxyaminoalkane.
The alkenylnitriles that react according to the present invention are those alkenylnitriles that are xcex1, xcex2 unsaturated. That is the double bond is in the 2 position relative to the CN group.
Particularly useful in the present invention are the 2-pentenenitriles. 2-Pentenenitrile, including the geometric isomers, react directly to form the adduct. The 3- and 4-pentenenitriles isomerize to 2-pentenenitrile under the reaction conditions of the present process to react to form the adduct. These pentenenitriles are by products in the manufacture of adiponitrile and are therefore cost effective starting materials. In the present process, these pentenenitriles may be reacted in mixtures, one with another or all three together, mixed any ratio or may be reacted as isolated compounds.
The benzyl alcohol is generally present in the reaction mixture at about a 2 to 1 molar ratio with the alkenyl-2-nitrile. The base is present in the range of from about 1 to 5% by weight of the reaction mixture.
Many bases are suitable for use in the present process, although ammonia and primary amines must be avoided. Suitable bases include bases selected from the group consisting of alkali metal hydroxides; alkaline earth metal hydroxides, alkali metal carbonates, alkaline earth metal carbonates, tertiary amines, Lewis bases and strongly basic ion exchange resins. It is also possible to use the base in a variety of physical forms. For example, the base may be used as a solution, as an aqueous solution, as solid particles or the base may be supported on solid particles. Solid forms of the base, for example, may be ground or flaked alkali hydroxides such a sodium, potassium or calcium hydroxide or particles of metal carbonates, such as potassium carbonate or calcium carbonate. The base may also be supported on a second particle such as potassium hydroxide deposited on clay, silica, alumina, titania or zirconia. The base may also be used as a (or in) solution either in an inert organic solvent or in water.
Hydroxyalkanenitriles formed in the present process are useful as starting materials for making various polymer classes; raw materials and intermediates for many organosynthesis products, such as pharmaceuticals; agricultural chemicals; a monomer for coatings; and polymer intermediates.
The soft or partial hydrogenation of the adduct to the 3-hydroxyalkanenitrile, is carried out in the presence of a trace amount of HCl over a platinum or palladium catalyst, usually supported. By trace amount of HCl is meant concentrations of HCl in the reaction mixture of from about 0.05 to about 1% by weight HCl.
The hydrogenation of the 3-hydroxyalkanenitrile to form the alkanolamine (or hydroxyaminoalkane) is typically carried out over metal catalysts such as RANEY nickel, RANEY cobalt, RANEY nickel or RANEY cobalt catalysts promoted with chromium, nickel, iron, molybdenum or mixtures of any of these metals (RANEY is a trademark of W. R. Grace and Company). The hydrogenation is typically run at temperatures of from about 75 to about 150xc2x0 C. and pressures from about 200 to about 4000 psig.
The present process may also be carried out with a solvent present, either alone or in combination with water, in the reaction mixture. Such solvent needs to be inert under the reaction conditions of the process. That is the solvent should not be a material or mixture that will add or otherwise react non-reversibly with the subject pentenenitriles. Preferred solvents include dioxane, tetrahydrofuran, dimethylformamide, dimethylacetamide, methanol, ethanol and isopropanol. Water may be present in the reaction solution. If water is present in the reaction, it is preferred that the water is present at not more than about 5% by weight of the reaction mixture. The most preferred concentration of water is about 2%. In the catalyst mixture used in this full hydrogenation, the catalyst mixture may contain up to 5 weight % aqueous caustic containing from 100 to 1000 ppm of an alkali metal or alkaline earth metal oxide or hydroxide.
The present process may be run a s a batch, semi-batch or a continuous process.
The present process is illustrated by the following examples. These Examples are not intended to limit the invention.